This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for operating gas turbine engines.
Gas turbine engines typically include an inlet, a fan, low and high pressure compressors, a combustor, and at least one turbine. The compressors compress air which is channeled to the combustor where it is mixed with fuel. The mixture is then ignited for generating hot combustion gases. The combustion gases are channeled to the turbine(s) which extracts energy from the combustion gases for powering the compressor(s), as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
When engines operate in icing conditions, i.e., exposed to clouds of super-cooled water droplets, ice may accumulate on exposed engine structures. More specifically, if engines are operated within icing conditions at low power for extended periods of time, ice accumulation within the engine and over exposed engine structures may be significant. Over time, continued operation of the engine, a throttle burst from lower power operations to higher power operations, and/or vibrations due to either turbulence or asymmetry of ice accretion, may cause the accumulated ice build-up to be ingested by the high pressure compressor. Such a condition, known as an ice shed, may cause the compressor discharge temperature to be suddenly reduced. In response to the sudden decrease in compressor discharge temperature, the corrected core speed increases in the aft stages of the high pressure compressor. This sudden increase in aft stage corrected core speed may adversely impact compressor stall margin. In some cases, it may also lead to an engine flame out.
To facilitate preventing ice accretion within the engine and over exposed surfaces adjacent the engine, at least some known engines include a de-icing system to reduce ice accumulation on the gas turbine engine struts. However, if the gas turbine engine component is fabricated using a composite material, it is relatively difficult to anti-ice the component using heated air that is channeled through the composite component due to low transverse thermal conductivity of the composite material. As result, relatively hot air is required to de-ice the component thus penalizing the overall engine efficiency.